1. Field of the Invention
This invention relates to a method for the dehumidification of air and to apparatus useful in practicing the method. Specifically, a super-absorbent polymer or another material which is capable of removing water vapor from air without releasing the latent heat of vaporization of the water vapor removed is employed for dehumidification. Examples of super-absorbent polymers that can be used for dehumidification according to the instant invention include lightly cross-linked hydrophillic polymers disclosed in U.S. Pat. No. 4,293,609 and in patents cited therein as disclosing such polymers and starch/acrylic graft copolymers disclosed in U.S. Pat. Nos. 4,338,371, 4,076,663, 4,055,184, 3,997,484, 3,661,815 and 3,425,971.
2. The Prior Art
Humidity control is an important part of heating, ventilating and air conditioning. In cold climates it is desirable to add moisture during the heating season and, in most parts of the United States, it is desirable to remove moisture whenever there is hot, humid weather. Some industries require both humidity and temperature to be controlled within relatively narrow limits whenever certain processes are being practiced; this may involve humidification or dehumidification and heating or cooling. Moisture vapor has been removed from air by contact with a cooled coil or with cold water, and also has been removed by chemical dehumidification, for example by contact with alumina, silica gel, an ethylene glycol solution or a lithium chloride solution.
When air is dehumidified by contact with a chilled coil, sensible heat is removed from the air until it becomes saturated with moisture vapor and, as the air is cooled further, both sensible and latent heat are removed; the result is air essentially saturated with water vapor. Many people find buildings air conditioned in this way uncomfortable, frequently characterizing them as "clammy"; further, in many instances, the limiting condition which determines the energy requirements of systems which dehumidify in this way is the energy requirement for dehumidification, because that amount of energy provides more sensible cooling than is required for comfort. In such cases, more effective insulation of the space being conditioned does not reduce the energy requirements for air conditioning because the same amount of energy is still required to accomplish dehumidification.
Chemical dehumidification can be used to provide air at any moisture level required for air conditioning, and independently of temperature. However, chemical dehumidification as presently practiced involves the evolution of heat in an amount equal to the latent heat of vaporization of the moisture removed from the air, so that sensible cooling is required both to remove the latent heat of vaporization of the water vapor removed and to lower the air temperature below ambient the amount required for temperature control. In addition, chemical dehumidification requires energy to regenerate the desiccant, i.e., alumina, silica gel, ethylene glycol or lithium chloride, and frequently requires sufficiently close control to necessitate an operator.